SNAILS AND THEIR SHELLS.

Thames Star, Volume LVII, 23 August 1923, Page 2

SNAILS AND THEIR SHELLS.

How does a snail make its shell? asks G. W. Bulman in Chamber’s Journal. The answer of science justifies the word “make”; the snail does make its shell. For the shell, it appears, does no i grow, like nails or hoofs, but is actually made, or built, by the animal inside. In the wonderful chemistry of the snail’s body, lime is separated from the food, and using its “mantle” as a sort of trowel the little mason spreads the mortar on the edge of the aperture—the lip, as it is called—of the shell. Very often in a specimen you can distinguish the new layer of shell from the old. And the new material is laid on so as to preserve the plan of the shell of the species to which it belongs—in our case that of the garden snail (Helix asper)—and no other. That is perhaps the most wonderful thing about it. There are so many thousand species of shell, and each snail builds its house after the special plan of its kind. An interesting experiment was once tried by some ingenious Frenchmen. They carefully removed snails of a certain species out of their shells, and put them into shells of the other species. When these had occasion to enlarge they did it on the lines of their old shells.

Natural selection, having, as it were, taken great pains to show us what a very useful thing, what a necessary thing a strong shell is for a soft animal, says in effect, “Not at all!” and points to the slug, which has, so to speak, thrown aside its shell as useless. And yet it keeps inside the folds of its mantle a minute model to show—perhaps!—thav its ancestors were snails.